Method and system for lithography simulation and measurement of critical dimensions

ABSTRACT

A method and system for lithography simulation is disclosed. The method and system specify a subject region of a lithography image with a CD marker, specify a threshold intensity over the lithography image, specify a gradient to a threshold value of the threshold intensity, and calculate a sensitivity or ratio of change of an image boundary of the lithography image to lithography process variation.

BACKGROUND

1. Field

The field of the present invention relates to lithograph technology forfine image fabrication, and in particular to a lithography simulationsystem and measurement of critical dimensions.

2. Description of Related Art

Fine image fabrication by lithography uses technologies like particlebeam writers for writing fine images on a plate coated by a particlebeam sensitive resist and an optical projection lithography method thatuses a mask having transparent and opaque parts on the surface of themask for generating a fine image on a plate coated by a photo sensitiveresist. An example of particle beam writers is an electron beam writerthat is used for writing fine images on both silicon wafers and masksfor optical projection lithography. A technology that uses electron beamwriters for making fine images for semiconductor integrated circuitsdirectly on the semiconductor wafer is called Electron Beam DirectWriting (EBDW) technology. EBDW technology is suitable for integratedcircuit fabrication that requires a quick turn around time.

A fundamental problem with conventional lithograph technologies is imagequality degradation and resolution limits caused by chemical andphysical effects in the process of the technologies. An example of suchphenomena is proximity effect, which occurs in both electron beamwriting and optical projection lithography and causes differencesbetween intended patterns and images obtained by the lithographytechnologies. This degradation of the image quality becomes serious whenthe image is finer. An accurate measurement of the image qualitydegradation or measuring differences between intended patterns andimages distorted by the proximity effects are important for accuratecorrection of the effects.

Measurement of critical dimension (CD) of the image at a predefinedpoint is important and called CD measurements. With reference tosemiconductor integrated circuits, as an example, CD measurement isconventionally done by Critical Dimension Scanning Electron Microscope(CD-SEM) after fabricating the image by the lithography. The CDmeasurement results are required before fabrication of the image.

To resolve the above mentioned issues related to conventional CDmeasurement, simulators for analyzing proximity effect have beendeveloped. Using these type of simulators, the degree of image qualitydegradation or differences between intended patterns and images obtainedby the lithography technologies becomes predictable without fabrication.This simulation method still has a problem, wherein these simulatorsconsume huge amounts of computing time for obtaining the lithographyimage for large area similar to a whole LSI chip. Specifying the CDmeasurement points is also tedious and time consuming work when theobjective area becomes large. Even if CD measurement results areobtained, the amount of data is huge, and it is difficult to understandthe result intuitively.

Another issue related to the lithography technology for fine imagefabrication is that the obtained image becomes sensitive to thelithography process parameters with progress of image miniaturization.The sensitiveness is referred to as lithography process sensitivityhereafter. The lithography process sensitivity depends on a position ofthe image and environment of the image. Although knowing lithographyprocess sensitivity at specified points of the image contributes tolithograph technology, no quick method is reported to calculate thelithography process sensitivity.

The conventional CD measurement equipment usage method, such as CD-SEM,as an example, is not efficient. The measurement points areconventionally specified by human engineers, wherein the selected pointsmight not be optimal in the sense of efficient use of measurementequipment. Selecting many measurement points is also difficult forengineers.

In light of the foregoing discussion, a method and system that improvesthe speed of lithograph simulation and simultaneously improves theefficiency and accuracy of the CD measurement of the image by lithographtechnologies is needed. The system should be capable of displaying hugeamounts of data obtained by the CD measurement effectively andintuitively. In one aspect, sharing of CD measurement related databetween the simulation and the equipment is required for the system toimprove efficiency and accuracy of the CD measurement. Although theconventional CD measurement methods focus on visible dimensions of theimage, finding potential risk points of the image is essential withreference to the high lithography process sensitivity region. The CDmeasurement method that uses the lithography simulation should supportsuch requirements.

SUMMARY

In the semiconductor manufacturing industry, lithography technologyenables printing of accurate and fine patterns on wafers or masks.Electron Beam Direct Writing (EBDW) method allows writing patterns on awafer by electron beam, and optical lithography (OL) methods enableprinting images by predefined masks. Differences between intendedpatterns and an obtained printed image are observed in both EBDW and OLcases, which are caused by chemical or physical processes like proximityeffect.

Computer simulation is an efficient means to investigate differencesbetween intended patterns and obtained images. CD (Critical Dimension)measurements that measure critical dimensions of the image based on thecomputer simulation results are important and helpful. CD measurementresults in conjunction with quality control of semiconductormanufacturing process can contribute yield improvement and efficientquality control.

To achieve the above mentioned objectives, the concepts listed belowcontribute to improvement of quality and accuracy of lithographytechnology: (1) a method and equipment for fast lithography simulationand CD measurement, (2) an effective method for specifying measurementpoints that are critical and to be checked with attention, (3) a displaymethod and equipment that is intuitively understandable, (4) a dataprocessing system and method that transfer information based on CDmeasurement results by simulation for controlling, guiding inspectionpoint finding, and helping inspection equipments, and (5) a method andsystem for calculating sensitivity of process variation to lithographyimage.

A calculation method enables calculation of simulation based CDmeasurement results with small computing time by using CD markers forreducing computational efforts is presented.

A CD marker setting method uses design hierarchies for reducing tediousmanual CD marker setting operations. The design hierarchy includeslibrary cells and blocks that are repeatedly used in the design.

A lithography process sensitivity concept enables indication ofpotentially critical parts of lithography images and a fast calculationmethod of the lithography process sensitivity. The method uses CD markerfor limiting calculation area for reducing computational time.

A CD measurement result display method and equipment for helpingintuitive understanding of distribution of CD measurement results isdisclosed. The resultant values are associated with geometrical displayof the lithography images.

An intuitive and efficient method specifies a region for calculatingpartial statistical quantities. The method allows specifying the regionfrom a display device showing images related to the layout.

A method improves efficiency and accuracy of dimensional inspections andmeasurement of products like wafers and masks. The method forwardsinformation generated from CD measurement simulation results and CDMarkers to the equipment.

These and other objects and advantages of the present teachings willbecome more fully apparent from the following description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows conventional lithography simulation and procedure of CDmeasurement by the simulation.

FIG. 2A shows one embodiment of CD Measurement and IC Layout.

FIG. 2B shows a part of the IC Layout of FIG. 2A.

FIG. 3 shows CD measurement categories P1˜P5.

FIG. 4 shows CD Marker and Evaluation points.

FIGS. 5A-5B show embodiments of a CD Measurement method.

FIG. 6 shows one embodiment of a flowchart for CD Measurement.

FIGS. 7A-7B shows sensitivity of an image to lithography variation.

FIG. 8 shows a flow chart for high sensitivity point detection.

FIG. 9A shows CD Markers embedded in a cell library.

FIG. 9B depicts relations between CD marker template in library data.

FIG. 10 shows a CD Marker selection by cell type.

FIG. 11 shows an example of CD Measurement result display.

FIG. 12 shows a conventional interface to measurement equipment.

FIG. 13 shows one embodiment of an interface to measurement equipment.

FIG. 14 shows one implementation example of transferring CD measurementinformation to inspection equipment.

FIG. 15 shows an example of virtual pattern generation.

DETAILED DESCRIPTION

Various embodiments of the present invention are described hereinafterwith reference to the drawings. It should be noted that the drawings arenot drawn to scale and that elements of similar structures or functionsare represented by like reference numerals throughout the drawings.

FIG. 1 shows conventional lithography simulation and procedure of CDmeasurement by the simulation. A target region 100 is an area wherelithography simulation is performed. A grid 102 for simulation is a setof points that covers the target region 100 and intensity of thelithography is calculated at the points. An image 104 of the lithographyobtained by the simulation, and contour 106 of the intensity.

Lithography is an indispensable technology for modern finemanufacturing. In the semiconductor industry, for example, it isrelatively difficult to build a semiconductor manufacture processwithout lithography technologies. Other examples include fabrication ofMEMS (Micro Electro-Mechanical System) and other micro-fabrications.

Although lithography is a strong technology for micro fabrication, it isnot perfect. One of the issues is the proximity effect that degradesimages obtained by the technology. The proximity effect is caused byinfluences of images placed near by, and changes the shape of theimages. The proximity effect is caused by chemical and physicallithography process and occurs in both optical lithography and alithography that uses a charged particle beam like an electron beam.More precisely speaking, the effect is caused by scattering of particleslike electrons and photons that penetrate into resist and collide withmolecules in resist and underlying materials.

To know the proximity effect by simulation is important forunderstanding how the degrading of the image occurs and for knowing themost effective way of the proximity effect correction. Hereafter, thissimulation is called lithography simulation.

Conventionally several proximity or lithography simulators have beendeveloped. However, it is not reported that those simulators can providegood quality images for sufficient area in a semiconductor application,such as, for example, a full chip region. Several studies on lithographysimulation have been reported for accomplishing high speed calculation.These examples of devices include an acceleration of convolutioncalculation that is required in lithography simulation by FFT (FastFourier Transform), reduction of computational amount by using irregularevaluation point mesh that is dense for steep intensity changing regionand is coarse for gradually intensity changing region, and so on.However, those devices are not satisfactory for users who needlithography image for a large domain.

In one aspect, the purpose of obtaining the image by a lithographysimulator is considered. FIG. 1 shows an example of practical use ofconventional lithography simulation results. Intensity of thelithography that is a quantity required to know, deposit energy for anexample, is calculated for each point of a grid that covers a targetregion 100. The calculated results of the intensity can be seen as shownby “Image by Simulation” 104 in FIG. 1. Moreover, it is required to knowhow the latent image is developed and seen on the resist. For suchcases, a contour tracking program can be used to draw contours 106 thatshow development threshold of the resist. Measuring quantitativedifference between image by lithography and the intended pattern atcritical point of the pattern is important for understanding accuracy ofthe lithography. This is called CD (Critical Dimension) Measurement 108and is commonly used for quality control of the wafer and maskfabrication. From quality control point of view, CD measurement 108 ismore important than viewing images by the lithography.

Detail of the CD measurement 108 will be described with reference tosemiconductor integrated circuits, as an example. FIG. 2A shows oneembodiment of CD measurement 120 with an example of a logic cell layout122, such as an integrated circuit (IC) layout, and FIG. 2B shows a part124 of the logic cell layout with P1˜P5 indicating CD markers.

FIG. 2A depicts an example of a layout for semiconductor integratedcircuits (ICs) and a concept of CD measurement. FIG. 2B shows a part ofthe integrated circuit (IC) layout 122 and a pattern 124 forpoly-silicon layer that is, for example, a gate of an MOS transistor. P1through P5 of FIG. 2B show examples of CD measurement categories. In oneembodiment, the meaning of each symbol is; for example, P1—gate length,P2—end cap or gate fringe, P3—gate position, P4—inner corner, P5—outercorner, respectively.

In the lithography process by the particle beam writing, many physicaland chemical effects give influence on images obtained on the resist.Such effect or variation includes temperature, chemical component ofresist, stability of e-beam gun, and other environmental conditions. Inone aspect, these variational effects are called lithography processvariation hereafter. By these variations, the image obtained by thelithography changes to some extent. It is required to estimate theinfluence of such variation to the image. The influence of the processvariation to the image varies depending on a position of the image. Itis difficult to evaluate each effect of the lithography processvariation, but representing variation of those effects by change ofthreshold of lithography intensity is a reasonable way. Lithographyprocess sensitivity is defined as influence of the threshold change tothe change of the lithography image.

FIG. 3 explains CD measurement categories with reference to CDmeasurement categories P1˜P5 of FIG. 2B.

P1˜P5 indicate categories for the CD markers. P1, for example, is acategory that measures line width. P2, for example, is a category thatmeasures shortening of line end. P3, for example, is a category thatmeasures absolute distance between obtained image and target patterns.P4, for example, is a category that measures rounding at a convexvertex. P5, for example, is a category that measures rounding at aconcave vertex.

In one aspect, categories P1˜P5 intend to measure differences betweenobtained images and intended patterns. In a case of lithographysimulation, evaluation of quantitative differences between imagesobtained by the simulation and intended pattern is important for qualitycontrol of the lithography.

In one aspect, CD measurement results in a number for quantitativequality control of the image obtained by lithography. Visiblerepresentation of a simulation result image, as shown in FIG. 1, forexample, is helpful for intuitive understanding of the result but is notnecessarily from qualitative quality control point of view.

FIG. 4 shows CD marker and evaluation points, and FIG. 4 explains detailof the CD marker, target pattern and evaluation points. In oneembodiment, the target pattern is required by the design, and the CDmarker is a geometrical entity that is a critical region required to bemeasured. In FIG. 4, AA′ and BB′ are examples of a CD marker, and theevaluation points are a set of coordinates where the lithographyintensity is calculated. As shown in FIG. 4, CD markers are assigned totarget patterns for indicating measurement points. In one aspect, AA′and BB′ are examples of CD markers that are represented by linesegments, for example.

In one embodiment, AA′ is an example of CD marker usage that isapplicable to the categories characterized by measuring distance betweenedges of the target pattern and image. P2, P4, and P5 of FIG. 3 areexamples of this type. BB′ is an example of CD marker usage that ischaracterized by measuring a difference between width of the image andthe intended pattern. P1 is an example of this type of CD Marker. P3 inFIG. 3 is an example that measures difference of position betweenintended patterns and obtained images.

In one aspect, FIGS. 5A-5B show embodiments of a CD measurement method,and a principle of CD measurement by this invention is illustrated.Curves called Simulation Result indicate intensity of the lithography(deposition energy in e-beam case) on line segments AA′ and BB′. Linegraphs called Target are ideal intensity distribution for the targetpatterns. Horizontal lines called Threshold indicate level oflithography intensity that generates the lithography images.

FIGS. 5A-5B depict details of how CD values are measured by theembodiments in which CD markers are set, as shown in FIG. 4. Positionalcoordinates of placed CD markers are indicated on a horizontal axis. AA′of FIG. 5A corresponds to AA′ in FIG. 4. Similar to the above example,BB′ of FIG. 5B corresponds to BB′ in FIG. 4. Vertical axis indicates anintensity of deposited energy of particles like electrons or photonsthat causes chemical reaction in the resist.

Intensity curves are calculated by simulation along with lines AA′ andBB′ and indicated by “Simulation Result” in FIGS. 5A and 5B. On theother hand, preferable intensity curves for getting the best images arestep functions as shown by “Target” in FIGS. 5A-5B. Resist is modeled ona simple “Threshold” that determines where image appears. In FIGS.5A-5B, image is developed in the area where intensity exceeds the“Threshold”. This is a simple model but behavior of the resist isdescribed. “CD Value” that is defined by the difference between targetpattern and image by lithography is measured as a distance between across point of “Target” line and “Threshold” line and a cross point of“Simulation Results” and “Target” line. In FIG. 5A, CD value is distancebetween X1 and X2, and in FIG. 5B, CD value is calculated based ondistances between X1′/X1″ and X2′/X2″.

In one aspect, the above description of CD measurement method indicatesthere is no need to calculate intensity of all grid points in the targetregion for calculating CD values. Calculation of intensity on the regionrelated to a CD marker is sufficient. By this invention, the number ofthe intensity calculation is drastically reduced. In one embodiment,this method can obtain the same CD measurement results withinapproximately 1/40˜ 1/90 of CPU time required for the conventionalmethod that is described in FIG. 1. In one embodiment, the hereindescribed method of the invention enables evaluation of specifiedcritical dimensions of lithography image for large regions like a wholechip that was impossible by the conventional method.

The following description is an example of the embodiment of the CDmeasurement system. It should be appreciated that there are many otherembodiments based on the invention. In one aspect, FIG. 6 shows oneembodiment of a flowchart for CD measurement. An example of CDmeasurement procedure is explained step by step in FIG. 6, wherein FIG.6 depicts one embodiment of a flowchart of the invention.

In one aspect, step (200) and (210) of FIG. 6 respectively indicate astart point and end point of a repetition. It should be appreciated thatsteps between (200) and (210) can be repeated for all CD markers in anobjective region.

In step (202), the intensity evaluation point(s) on the CD marker linesegment is (are) determined.

In step (204), intensity of lithography on the point(s) determined instep (202) is (are) calculated.

In step (206), a threshold of the intensity and the intensity calculatedin step (204) is compared.

In step (208), a point at which the intensity is equal to the thresholdis stored in memory. In one aspect, storing formats of the point datafor this step depend on the category of the CD measurement. An qualitycheck can be accomplished by step (206). If the equality check is notsatisfied, step (208) will be skipped.

In step (212), CD values are calculated based on both the pointinformation stored at step (208) and the category specified by the CDmarkers. In one aspect, examples of the category are depicted as P1˜P5of FIG. 3.

In one embodiment, lithography process sensitivity is a type of CDvalue. Different from category P1˜P5 that are calculated based onintensity-threshold equivalent point information, the lithographyprocess sensitivity is calculated based on an idea related todifferential calculus. In lithography technology, gradient of theintensity curve near the threshold value is important. The sensitivitythat is defined as influence of process variation to the image by thelithography (hereafter called lithography process sensitivity) decreaseswhen the intensity curve is steep. In other words, the shape obtained bythe lithography changes largely when the intensity curve is gradual.

The CD measurement method by this invention is applicable for the abovementioned lithography process sensitivity check. A questionable areafrom lithography process sensitivity point of view is a region whereΔI/distance (P1,P2) is less than a specified value, P1 is a point whereintensity of the lithography is equal to the threshold, and P2 is apoint where intensity of the lithography is equal to the threshold+ΔI,where ΔI is a specified small value compared with the threshold value.This type of CD measurement is conventionally not easy to performbecause the point where the intensity is equal to threshold+ΔI isdifficult to observe in the resist. In one aspect, the CD measurementmethod by this invention allows estimation of this type of value byvirtue of simulation base method.

FIGS. 7A-7B show sensitivity of an image to lithography processvariation. How process variations influences images obtained bylithography technologies is depicted in FIGS. 7A-7B. FIG. 7A shows, forexample, a case where the intensity curve is steep at the cliff of theintensity. FIG. 7B shows a case where the intensity curve is gradual. Inone embodiment, lower charts of FIGS. 7A and 7B show intensity curves online AA′ and BB′, threshold levels, and threshold+ΔI level, and uppercharts of FIGS. 7A and 7B show how the images that are developed in bothcase.

FIGS. 7A-7B depict how process variations influences images obtained bylithography technologies. In case of FIG. 7A, intensity curve is steepso that influence of the process variations on the images is relativelysmall. In case of FIG. 7B, gradient of intensity curve is gradualcompared with case 7A, so that the image changes caused by lithographyprocess changes (one example is variation of resist temperature) arelarger than case 7A.

In FIGS. 7A and 7B, X-Y coordinates of upper chart of FIGS. 7A and 7Bindicate geometrical positions on a plane coated by resist, andrectangles indicate the images obtained by lithography technologies. Onthe other hand, X-Y coordinates in lower part of FIGS. 7A and 7Bindicate intensity of the lithography and geometrical positions on lineAA″ and BB″. Image appears where intensity of energy, for example,exceeds predefined threshold. In one aspect, the threshold of theintensity varies depending on states of resist and other processparameters like temperatures. FIGS. 7A and 7B explain a case in that thethreshold intensity decreases ΔI by variation of some processparameters. In case the threshold intensity decreases, intersections ofthe intensity curve and the threshold will shift from A′ to A″ and B′ toB″. As a result of threshold shift, a boundary of the image moves to apoint of Δx right, and the image becomes large. In case of FIG. 7B, theboundary of the image also moves to a point of Δx′ right, and the imagebecomes large. As a conclusion of the discussion on FIGS. 7A and 7B,Δx<Δx′ or the boundary move of (A) is smaller than that of FIG. 7Bbecause the intensity curve for FIG. 7A is steeper than that for FIG.7B.

Based on above mentioned invention and principle, a system can beimplemented that reports a subset of regions specified by CD markersthat have potential risk of generating poor images because of the highlithography process sensitivity. The region where a distance betweenP(T) and P(T+ΔI) is larger than a specified value related to the ΔI willbe reported, where P(T) is a cross point of the intensity curve andthreshold line, and P(T+ΔI) is a cross point of the intensity curve andthreshold+ΔI line on a CD marker line. This check is useful foridentifying regions where generated images are potentially unstable forprocess variation in other word lithography process sensitivity is high.

FIG. 8 shows a flow chart for high sensitivity point detection, and anexample of lithography process sensitivity procedure is explained by aflow chart in FIG. 8. The sensitivity can be calculated as a part of CDmeasurement.

An embodiment of lithography process sensitivity calculation methodbased on the invention is described below. This is an example of theembodiment of the invention; other embodiments are also possible. Themethod and flow by the invention are described by FIG. 8.

Step 300: Calculation of point P (I_(T)) and P (I_(T)+ΔI) on a specifiedCD Marker is done, where P(I_(T)) is a cross point of the intensitycurve and threshold line I_(T) and P (I_(T)+ΔI) is a cross point of theintensity curve and threshold+ΔI.

Step 302: Calculation of ΔD=distance between P (I_(T)) and P (I_(T)+ΔI)is performed, that is a distance between edges of the lithography imagesassuming I_(T) and I_(T)+ΔI as threshold values.

Step 304: Check whether calculated the distance ΔD of the step 302 isbigger than provided criteria. ΔD/ΔI is an index that indicatesdeviation of the image by the threshold changes caused by thelithography process variation. Risk of the image deviation increaseswith increase of the sensitivity.

Step 306: This is a step that checks completion of processing whole CDMarkers. Loop 308 is a loop for repeating the remaining processes for CDMarkers.

The lithography process sensitivity calculation method, as shown in FIG.8, is an example of the embodiment and other embodiments using step 300,step 302, and step 306 can be possible.

The CD measurement of images by lithography technology can be performedquickly by the above mentioned methods. Efficient assignment of CDMarkers at appropriate points is another issue. A method by conventionalthinking is using layout database flattened by software and placing themarkers at critical points by hand. However, it is tedious and timeconsuming to place CD markers at all critical points on a chip.

To resolve above mentioned marker assignment problem, the followingmethod and system are disclosed. By the disclosed method, templates ofCD markers are associated with critical points of polygons in librarycells in advance, and a CD marker is generated based on the template toa position where the cell is placed and instantiated. By the mentionedmethod, the CD marker marking becomes effective because preparing thetemplates for a library cell makes possible to repetitively generate CDmarkers where cells are placed. In one example, to embody the mentionedmethod, (1) embedding templates for CD markers in library cells and (2)generating CD markers at where the cells are placed, are required.

An embodiment of the disclosed method is control of CD marker generationby human operators' directions, which will be described in followingsection.

FIG. 9A shows CD markers embedded in a cell library, and FIG. 9B depictsrelations between CD marker template in library data, and how thesetemplates are used in the design. FIG. 9A indicates a library wherecells or blocks repetitively used are stored. FIG. 9B indicates a designthat uses cells in the library. Cell 1 and Cell 2 are example names ofthe library cells. CD marker templates are associated with these librarycells. In one aspect. both Cell 1 and Cell 2 are instantiated two timesin design FIG. 9B.

In one aspect. FIG. 9A shows a library database in where cells, that maybe used by a design, are stored. FIG. 9B shows an example of a design.In the example, both Cell A and Cell B are used twice for implementingthe design. 4 times assignment of CD markers are required if no designhierarchy information is used, as shown in FIG. 9B. In case of usingdesign hierarchy like cell library, same CD marker assignment isperformed by preparing two CD marker templates. Effect and operation ofthe method is explained by an example. A cell in the library issometimes referenced more than thousands times in a common design. Insuch case, reduction of time and effort for the CD marker assignment islarge.

FIG. 10 shows a CD marker selection by cell type. Generation of a CDmarker is controlled by Cell name. FIG. 10 is an example that CD markersfor cell 2 are not generated. FIG. 10 is an example that depicts meritof specifying template of the CD Marker by name of the cell type whetherto generate CD Marker or not. Precise specification of cell instancesfor CD measurement can be doable by identifying it by cell types. FIG.10 corresponds to FIG. 9B. Two instances of Cell 2 type in FIG. 10 areomitted from the evaluation objectives. The elimination operation can beeasily performed by specifying cell types but not specifying cellinstance one by one. Furthermore, using categories appeared in FIGS. 3and 4 with the invention depicted in FIG. 10 allows more complexspecification of CD measurement objectives. By virtue of this efficientfiltering capability, it is more efficient to focus on a spot ofinterest and reduce computation time by eliminating unnecessaryevaluation points.

FIG. 11 shows an example of a CD measurement result display. Both layoutand CD measurement results are displayed on a same screen. The value ofthe CD measurement results is indicated by color. (1) Partial statisticsreport shows statistic of a specified region. (2) StatisticalCalculation Region indicator is used for specifying a region for thecalculation. (3) Object Region is a region for the simulation. (4) ColorScale is used as a scale for the value of the CD measurement. CDmeasurement results are statistical quantities like average and standarddeviation, and generally calculated for whole objective area. Partialstatistical quantities of specified region are of interest forunderstanding result of dose correction.

FIG. 11 is an example of the display that are intended to fulfill one ormore of the above mentioned requirements.

In one example, quantity of CD measurement results is displayed with ageometrical entity that is related to the CD marker. An example of theembodiment is using color for showing the quantity and polygon of theLSI layout for geometrical entity. FIG. 11 is an implementation thatuses color and a rectangle related to the place of CD marker fordisplay. By this display, a user of the system can intuitivelyunderstand CD measurement results.

In another example, partial statistical report generation capability isshown in FIG. 11. This capability allows the user to specify a regionand to know partial statistical characteristics of the specified region.To satisfy such a requirement, the capability comprises a means forspecifying one or more region(s) for statistical calculation,calculating statistical quantities of the specified region, and a meansfor displaying the calculation results. A system may comprise the abovementioned components.

FIG. 11 shows a statistical result display device as an embodiment. (1)Partial Statistic Report shows statistical calculation results forspecified region. (2) Statistical Calculation Region Indicator shows aboundary of the region for statistical calculation. (3) Objective Regionindicates whole area for the calculation. (4) Color Scale indicatesquantitative result by CD measurement.

In one aspect, CD measurement result by lithography simulation is usefulas a feedback to the engineers and is also helpful to improve design,proximity effect correction, dose correction, and RET (ResolutionEnhancement Technology). Other uses of the CD measurement result assistsinspection and measurement of real lithography images by CD SEM, forexample.

FIG. 12 shows a conventional interface to measurement equipment andshows a conventional process from the manufacturing data generationthrough the inspection. For example, data 1 shows manufacturing datagenerated by CAD equipment. Manufacturing is performed at Step 401.Inspection points for checking whether the product satisfies quality andspec are prepared and transferred to the inspection equipment at step402. Inspections are done at step 403 according to the directionprepared at step 402. From the described procedure, the conventionalmethod for inspection cannot use useful information that is generatedwith Data 1 preparation. To resolve this issue, a new method isintroduced, as shown in FIG. 13.

FIG. 13 shows one embodiment of an interface to measurement equipment.Interface method of design information to inspection equipment by thisinvention is described. The design information includes lithographysimulation results and CD marker information.

In the method depicted by FIG. 13, directive data for the inspectionequipments is prepared using lithography simulation results 500, layoutdesign data 502, and CD marker information 504. In one embodiment, thedirective information including CD marker and geometrical shapes areprovided to the inspection equipment, for example, CD SEM for automaticnavigation of the equipment. Prioritizing CD markers can be based on thelithography simulation. The inspection or measurement is performed fromhighly prioritized CD markers to improve efficiency of the inspection.Effectiveness of the inspection can be improved by finding highlithography process sensitivity parts using the methods depicted byFIGS. 7A and 7B and transferring it to the equipment. The method isbased on an idea of understanding which part of the design is lessstable by using the simulator.

FIG. 13 shows an example of the interface method to measurementequipment by one aspect of the invention. The inputs of the methods areDesign Layout (502), results of lithography simulation (500), and CDMarker library (504). The output of the method is a directive to theequipment. The directive information controls an inspection equipment ina effective manner. That means minimize or at least reduce themeasurement time required to measure the critical dimensions. In step505, a set of measurement positions on a chip is determined using a setof information shown by 500, 502, and 504. In one aspect, Prioritizationor selection of the points can be done from efficiency point of view,for example, at step 505. In step 506, a chip level coordinateinformation is transformed in a wafer level because measurement orinspection of the fabricated chip is done on a wafer.

FIG. 14 shows one implementation example of transferring CD measurementinformation to inspection equipment, and FIG. 14 depicts an embodimentby the invention. In one aspect, Data 1, Step 601, Step 602, and Step603 are identical to that of FIG. 12. Step 4 is a step that createsvirtual pattern by the lithography simulation and the CD markers.

In one embodiment, as shown in FIG. 14, a virtual pattern 604 isgenerated and helps the inspection. Data 1 is manufacturing data and aproduct is manufactured at step 601 using the data. In step 602, CDmeasurement information like inspection points is transferred to aninspection equipment at step 603.

FIG. 15 shows an example of virtual pattern generation. A method forgenerating virtual pattern is described.

FIG. 15 depicts an example of generating virtual patterns for theinspection equipment. In one example. a virtual pattern may comprise aclosed polygon generated based on line segments TP1-A′ and TP2-TP3. TP1,TP2 and TP3 are points on CD marker lines and lithography intensityequal to the threshold. These virtual patterns are sent to the equipmentand used for helping the inspection.

At the inspection equipment, the above described virtual patterns areuseful for the following purposes. (1) A pointer helps visual check byoperators and is also helpful for indicating a next checking object. (2)References for comparison are useful because the virtual patterns aregenerated based on lithography simulation, and they indicate a line edgeof the lithography images.

In conventional lithography simulation, all grid points of an objectdomain are to be evaluated for getting intensity of the lithography. ForE-beam case the intensity is deposition energy. Image generated by thelithography is conventionally obtained by a contour line trackingprogram that finds out equi-threshold intensity points for the imagedevelopment and connects those points. The conventional method is timeconsuming. The method by this invention can significantly reducecomputation time by focusing the computing domain using CD markers.

Assignment of the CD markers to regions of interest is required forabove mentioned invention. In real mask fabrication and waferproduction, the number of CD measurement points is limited because ofrequired time for evaluation. In one aspect, the CD measurement by theinvention has a merit that allows a huge number of measurements comparedwith the conventional real measurement. In general, it requires apreparation of huge CD markers that number is equal to the measurementpoints. In another aspect, the invention embeds a template for a CDmarker into a library cell or block, which reduces time for CD markerassignment. This improves efficiency of the CD marker setting.

Lithography process sensitivity that indicates influence of lithographyprocess variation to the obtained lithography image is a conventionallyused idea. However, the conventional method requires evaluation of allgrid points of an object domain. Different from conventional methods,the method by the invention can calculate the sensitivity effectively byusing a method for CD Measurement. The calculation is effective andquick because it is done in the limited area specified by the CD marker.

In conventional CD measurement that is used for measurement of realmasks and wafers, the measurement points are so small that few need ofvisual display of the result is said. However, the above mentionedtechnology invokes a need for intuitive understanding. in contrast, thedisplaying method by the invention enables visual understanding ofrelation between CD measurement results and layout image. For someusers, it is useful to know partial statistical quantities like averageand standard deviations. The method by the invention uses layout imagedisplay and means for specifying a region for the partial statisticalcalculation, which allows users a convenient means of giving directions.Conventionally, there is no such way of the specifying area for thecalculation.

CD measurement is an important activity that is used for analyzingissues in a fabrication process and a judgment of whether a product isgood or not. Unfortunately, in conventional system, decision of pointsfor CD measurement is independently done in the manufacturing process.This invention enables providing the CD measurement activity with CDmarkers and related data from the design side. Moreover, the inventionenables prioritizing and sorting CD Markers for effective CD measurementby using lithography simulation results in design domain.

In one embodiment, the methods disclosed herein by the invention areapplicable for a simulation of mask and wafer writing by electron beamlithography, and are also applicable for the simulation of mask andwafer writing by more general charged particle beam writing.

In another embodiment, the methods disclosed herein by the invention arealso applicable for the simulation of the mask and wafer writing byoptical lithography.

In another embodiment, the methods disclosed herein by the invention areapplicable to, but not limited to, mask and wafer writing but also formore general lithography technologies.

Although particular embodiments of the present inventions have beenshown and described, it will be understood that it is not intended tolimit the present inventions to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present inventions. The specification and drawings are, accordingly,to be regarded in an illustrative rather than restrictive sense. Thepresent inventions are intended to cover alternatives, modifications,and equivalents, which may be included within the spirit and scope ofthe present inventions as defined by the claims.

1. A computer-implemented method for lithography simulation comprising:associating a template with a critical point of a shape in a librarycell stored in a library database; specifying a subject region of alithography image with a CD marker, wherein the CD marker is generatedbased at least in part upon the template to a position where the librarycell is placed and instantiated; specifying a threshold intensity overthe lithography image; calculating an intensity of the lithography imagewithin the subject region defined by the CD marker; specifying thesubject region for statistical calculation; performing the statisticalcalculation for the subject region; and displaying the subject regionand a statistical result of the calculation based at least in part uponthe subject region together on a same screen of a display device.
 2. Themethod of claim 1, wherein the CD marker includes at least geometricalinformation for defining the subject region.
 3. The method of claim 1,wherein the CD marker includes category information that determines anevaluation method used for CD measurement.
 4. The method of claim 1,wherein the subject region of the CD marker is defined by at least oneline segment.
 5. The method of claim 1, wherein a threshold value of theintensity for generating a image is specified and a sensitivity or ratioof change of an image boundary of the lithography image to lithographyprocess variation is calculated.
 6. A computer-implemented method for CDmeasurement calculation comprising: associating a template with acritical point of a shape in a library cell stored in a librarydatabase; calculating lithography intensity on a region or line segmentdetermined by a CD marker, wherein the CD marker is generated based atleast in part upon the template to a position where the library cell isplaced and instantiated; determining a point when lithography intensityequals a threshold; calculating a value of CD measurement based at leastin part upon information related to the determined point; specifying theregion or line segment for statistical calculation; performing thestatistical calculation for the region or line segment; and displayingthe region or line segment and a statistical result of the calculationbased at least in part upon the region or line segment together on asame screen of a display device.
 7. The method of claim 6, wherein thepoint and the value are simultaneously displayed on the display device.8. A lithography process sensitivity calculation system comprising: aprocessor programmed for: associating a template with a critical pointof a shape in a library cell stored in a library database; specifying anobjective region with a CD marker, wherein the CD marker is generatedbased at least in part upon the template to a position where the librarycell is placed and instantiated; specifying a threshold intensity over adeveloped lithography image; calculating a sensitivity or ratio ofchange of an image boundary to lithography parameter variation;specifying the objective region for statistical calculation; performingthe statistical calculation for the objective region; and displaying theobjective region and a statistical result of the calculation based atleast in part upon the objective region together on a same screen of adisplay device.
 9. The system of claim 8, wherein the system evaluatesthe influence of lithography process variation to the lithography imageobtained by lithography.
 10. A lithography process sensitivitycalculation method for evaluating lithography process variation to animage obtained by lithography, the method comprising: associating atemplate with a critical point of a shape in a library cell stored in alibrary database; specifying a region of a lithography image with a CDmarker, wherein the CD marker is generated based at least in part uponthe template to a position where the library cell is placed andinstantiated; determining a first point when lithography intensityequals a threshold; determining a second point when lithographyintensity equals the threshold plus a specified gradient value of thelithography intensity; calculating a distance between the first andsecond points; specifying the region for statistical calculation;performing the statistical calculation for the region; and displayingthe region and a statistical result of the calculation based at least inpart upon the region together on a same screen of a display device. 11.The method of claim 10, further comprising evaluating the influence oflithography process variation to the lithography image obtained bylithography.
 12. A computer-implemented method for lithographysimulation comprising: calculating a difference between a designedpattern and an obtained image from lithography technology at a specifiedpoint, wherein the specific point is generated based at least in partupon a template to a position where a library cell is placed andinstantiated; associating template information of the specified pointwith a library cell and a block of the designed pattern; specifying aregion for statistical calculation; performing statistical calculationfor the region; and displaying the region and a statistical result ofthe calculation based at least in part upon the obtained image togetheron a same screen of a display device.
 13. The method of claim 12,wherein an application of the template to the library cell or block iscontrolled by a template name.
 14. A computer-implemented method fordisplaying a CD measurement result on display equipment, the methodcomprising: associating a template with a critical point of a shape in alibrary cell stored in a library database, wherein a CD marker isgenerated based at least in part upon the template to a position wherethe library cell is placed and instantiated; specifying a region forpartial statistical calculation; performing partial statisticalcalculation for the region; specifying or showing a statistical resultof the partial statistical calculation; displaying a symbol of a layoutthat includes one or more points for the CD measurement result, whereinthe CD measurement result is based at least in part upon the CD marker;and displaying the region, the statistical result, and the CDmeasurement result together on a same screen of the display equipment,wherein the result comprises at least one result value that isassociated with the symbol of the layout.
 15. The method of claim 14,wherein the symbol and the at least one result value are simultaneouslydisplayed on the display equipment.
 16. The method of claim 14, whereinthe CD measurement results are indicated with a value associated with atleast one of color, chroma and brightness of color.
 17. The method ofclaim 14, wherein the CD measurement results are indicated with a valueassociated with at least one contour line.
 18. A computer-implementedmethod for measuring dimension of an image generated by lithographytechnology that uses a set of files having CD marker information, themethod comprising: associating a template with a critical point of ashape in a library cell stored in a library database; specifying ameasurement point by geometry; specifying information associated withresults of lithography simulation using the CD marker information,wherein the CD marker is generated based at least in part upon thetemplate to a position where the library cell is placed andinstantiated; specifying information derived from manufacturing data;specifying a region for statistical calculation; performing statisticalcalculation for the region; and displaying the region and a statisticalresult of the calculation based at least in part upon the informationtogether on a same screen of a display device.
 19. A computer readablemedium storing a computer program comprising instructions which, whenexecuted by a processing system, cause the system to perform a methodfor lithography simulation comprising: associating a template with acritical point of a shape in a library cell stored in a librarydatabase; specifying a subject region of a lithography image with a CDmarker, wherein the CD marker is generated based at least in part uponthe template to a position where the library cell is placed andinstantiated; specifying a threshold intensity over the lithographyimage; calculating an intensity of the lithography image within thesubject region defined by the CD marker; specifying the subject regionfor statistical calculation; performing the statistical calculation forthe subject region; and displaying the subject region and a statisticalresult of the calculation based at least in part upon the subject regiontogether on a same screen of a display device.
 20. The medium of claim19, wherein a threshold value of the intensity for generating a image isspecified and a sensitivity or ratio of change of an image boundary ofthe lithography image to lithography process variation is calculated.21. A computer readable medium storing a computer program comprisinginstructions which, when executed by a processing system, cause thesystem to perform a method for CD measurement calculation comprising:associating a template with a critical point of a shape in a librarycell stored in a library database; calculating lithography intensity ona region or line segment determined by a CD marker, wherein the CDmarker is generated based at least in part upon the template to aposition where the library cell is placed and instantiated; determininga point when lithography intensity equals a threshold; calculating avalue of CD measurement based at least in part upon information relatedto the determined point; specifying the region or line segment forstatistical calculation; performing the statistical calculation for theregion or line segment; and displaying the region or line segment and astatistical result of the calculation based at least in part upon theregion or line segment together on a same screen of a display device.22. The medium of claim 21, wherein the point and the value aresimultaneously displayed on the display device.
 23. A computer readablemedium storing a computer program comprising instructions which, whenexecuted by a processing system, cause the system to perform alithography process sensitivity calculation method for evaluatinglithography process variation to an image obtained by lithographycomprising: associating a template with a critical point of a shape in alibrary cell stored in a library database; specifying a region of alithography image with a CD marker, wherein the CD marker is generatedbased at least in part upon the template to a position where the librarycell is placed and instantiated; determining a first point whenlithography intensity equals a threshold; determining a second pointwhen lithography intensity equals the threshold plus a specifiedgradient value of the lithography intensity; calculating a distancebetween the first and second points; specifying the region forstatistical calculation; performing the statistical calculation for theregion; and displaying the region and a statistical result of thecalculation based at least in part upon the region together on a samescreen of a display device.
 24. The medium of claim 23, wherein theprocessing system, using a processor, evaluates the influence oflithography process variation to the lithography image obtained bylithography.